How many non-prescription drugs have become prescription drugs?

When I had sciatica I was in so much pain I couldn't even lie down.
The only over-the-counter medication that enabled me to go back
to work was ketoprofen. I tried ever other type available at the time.
It was sold back then under the Actron brand name. Later I had
another episode of sciatica and could not find Actron but instead
used another brand named Orudis KT. Now I see that it is no longer sold.

When I had a cold I usually took pseudoephedrine which not only stopped
the symptoms but actually made me feel energetic. It was sold under the
brand name Actifed. I started to suspect this was not a good drug when
a co-worker of mine was taking it all the time (and it also seemed to
cause my sinuses to permanently drain into my throut rather than
into my nose). Later I found out it was being used by teens to make
methamphetamines and it was pulled off the shelves. What really
annoyed me though is that Actifed is still sold under the same
brand name even though it has different ingredients now.

What are the FDA guidelines for testing of non-prescription vs.
prescription drugs on humans?

Is it easier for a pharmeceutical company to release for sale a
non-prescription drug than a prescription drug?